Question

Write any 4 important features of a DNA structure

Answer 1

1. The DNA is a right handed double helix. It consist of two polyribonucleotide chains (strands) twisted around each other on a common axis.
2. The two strands are antiparallel i.e., one strand runs in the 5’ to 3’direction while the other in 3’ to 5’ direction.
3. The width(or diameter) of a double helix is 20 A ˚(2nm).
4. Each turn (pitch)of the helix is 34A˚(3.4nm) with 10 pairs of nucleotides, each pair placed at a distance of about 3.4 A ˚(0.34nm)
5. Each strand of DNA has a hydrophillic deoxyribose phosphate backbone on the outside(periphery) of the molecule while the hydrophobic bases are stacked inside(core).
6. The two polynucleotide chains are not identical but complementary to each other due to base pairing.
7. The two strands are held together by hydrogen bonds formed by complementary base pairs. The A-T pair has 2 hydrogen bonds while the C-G pair has 3 hydrogen bonds. The G-C is stronger by about 50% than A-T.
8. The hydrogen bonds are formed between a purine and pyrimidine only. The only base arrangement possible in DNA structure is A-T, T-A , G-C, C-G.
9. The complementary base pairing in DNA helix proves Chargaff’s rule. The content of adenine equals to that of thymine and guanine equals cytosine.